1. Field of the Invention
This invention relates to a method and apparatus for automatically reducing background density in a designated area of a document sheet when reproducing the document sheet. The invention provides particular utility in electrostatographic reproduction apparatus and methods.
2. Description of the Related Art
Digital monochrome copiers have the ability to perform an "Auto Exposure" feature that is used to automatically sense the background intensity of an original with a non-white background and adjust the background to become white. A typical example of this feature is an operator trying to copy an original that has black text on a green background such as an income tax form. Without the feature, the original would print with an undesirable gray background. The operator may be able to get rid of the background gray with several empirical adjustments to exposure and contrast; however, this is inefficient. An Auto Exposure feature allows the operator to automatically make this adjustment simply by selecting the feature.
Traditionally, Auto Exposure features are limited for several reasons. First, the background is only sensed at a fixed position on the platen allowing the feature to be easily fooled, typically by an inexperienced operator not placing the original in the correct place on the platen where the sample takes place or by using an undersized original. Second, typically only a small number of samples are taken making the feature susceptible to error because of the limited amount of data the algorithm decisions are made from. Third, the feature is perforated over the entire original image, whereas only a portion of the image requires adjustment of background.
It is therefore an object of the invention to provide an electronic copier apparatus and method which overcomes the disadvantages of the prior art.